This invention relates to track circuits, and in particular, to continuous rail track circuits having termination shunts at each end.
In order to promote the general welfare and reduce the possibility of injury to life and property, it is conventional to provide a variety of signals, alarms and safeguards at intersections of highways and railroads. These alarms, signals and safeguards are very common and there are probably few, if any, automobile drivers who have not seen these devices at railroad intersections.
In order to provide an automatic alarm signal, it is necessary to detect the presence of a railroad vehicle. For many decades, circuits called track circuits have been used for such detecting purposes and a wide variety of track circuits have been developed. Some track circuits depend upon sections of track which are electrically isolated from adjacent sections. Track circuits detect the presence of a railroad vehicle by detecting that there is an electrical shunt from one rail to the other. Corrosion on the rail, atmospheric conditions, the quality of rail joints, leakage currents between the tracks, as well as a multitude of other factors, with which those experienced in the art are familiar, influence the sensitivity of the track circuit to the detection of a railroad vehicle.
In prior art systems, insulated joints have been used to define the end of a track section and such techniques have generally provided the most satisfactory track circuits for use in connection with highway intersections and for use in connection with railroad switching. However, installing and maintaining satisfactory insulated joints introduces a host of other problems which are familiar to those in the industry.